NMR Line Shape for a Rectangular Configuration of Nuclei

We present an approach to describe nuclear magnetic resonance absorption of dipolar-coupled rectangular configuration of nuclear spins associated with reorientation of ethylene bridge (–CH₂–CH₂–) in the crystal. The approach was applied to investigate reorientational mobility of dabco-linkers (1,4-diazobycyclo2,2,2]octane) in metal–organic framework Zn₂(bdc)₂(dabco)] (bdc—benzenedicarboxylate). Dabco rotation around the N–N axis is shown to remain down to 80 K and the activation energy of the molecule reorientation does not exceed 12 kJ/mol.